Iraj,

Some things to check:
1. Did you connect the AD7730 as is shown on p. 25 of
the datasheets(the DC connection)?
2. Do you have a crystal connected(ADC is delta sigma)?
3. I assume you meant RDY instead of DRY, also what
about the POL line(tied high or low)?
4. Are SYNC and RESET tied high?

If these things are taken care of, then you are left with taking a look at the CLK, DI, DO, and CS lines with respect to each other using a digital oscilloscope.


Regards,

Jacob